JPS6057364B2 - How to clean sulfur dioxide gas from a gas stream - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a first circulation system (coolant circulation system) for flue gas desulfurization that optimizes the use of make-up water while controlling slurry concentration for cleaning efficiency and cooling. ″・system),
The other concerns the operation of the gas stream cooler-absorber with a unique double circulation βO2 cleaning method, which is the second circulation system (absorbent circulation system).

The method of cleaning boiler flue gases with a slurry containing alkaline solids such as limestone (CaCO) or calcined limestone products, lime and hydrated lime is effective in removing sulfur dioxide gas (SO2) from these combustion gases. This is a well-known method. However, standard cleaning methods require significant amounts of make-up water to operate, thereby increasing the water requirements of the overall system. Because water of adequate quality is often available in limited quantities in equipment, cleaning methods require the use of a minimum amount of high quality make-up or reuse water. The sulfur dioxide scrubbing process requires make-up water to replace water lost primarily in two ways.

(2) unreacted drug, calcium sulfite hydrate, and calcium sulfate hydrate discharged from the system; This is the water lost with the discharge of solid waste consisting of slurry. Therefore, by reducing these water losses, the total replenishment water requirement to the system can be minimized. By controlling the circulating water from the dewatering system and selectively using high and low solids content slurry streams from the second circulation system (absorbent circulation system), we
It has been discovered that the aqueous slurry (coolant slurry) concentration can be controlled and the requirement for fresh make-up water can be reduced.

2. A process according to claim 1, wherein the solids disposed of in the double circulation carpenter [d-4] are primarily calcium sulfate. 7. The method of claim 1, wherein the low solids content stream from step [d] is primarily water and calcium carbonate.

8. The method of claim 5, wherein the high solids content understream is primarily water, calcium sulfite, and calcium sulfate. 9 (a) in a first circulation system (coolant circulation system), the gas stream is cooled with a first aqueous slurry containing alkaline solids; (b) in a second circulation system (absorbent circulation system), the gas to be cooled; washing the stream with a second aqueous slurry containing alkaline solids separate from the first aqueous slurry; (c) increasing the alkali solids content in the second aqueous slurry to a level between 6 and 14% depending on the sulfite gas content in the gas stream; (d) maintain the alkali solids content in the first aqueous slurry at a level of 3% or more depending on the sulfur dioxide content in the gas stream; removing and retaining one or both of alkali solids and water from a second aqueous slurry portion having an alkali solids content above or below said level. A method of operating a gas stream cooler-absorber comprising two circulation systems as claimed in claim 1.

10 The alkaline solid consists of CacO3 and is also new. A concentrated slurry of water and alkaline solids is introduced into the second aqueous slurry, and a circulating slurry is introduced into the second aqueous slurry to avoid the formation of dissolved calcium sulfate compounds in the second aqueous slurry and to form a substantially open second circulation system. 2 The first water is extracted from the aqueous slurry! 10. The method according to claim 9, wherein the method is incorporated into a synthetic slurry.

11 slurry is continuously fed from the second aqueous slurry to the first aqueous slurry to partially replace the slurry lost in the cooling process - Claim 1
The method described in item 0.

12. The method of claim 11, wherein the first aqueous slurry and the second aqueous slurry are circulated in separate cooling and cleaning circuits.

13 The cleaning of the gas stream is carried out in a closed vessel where the gas enters at the bottom and exits at the top, a first aqueous slurry is sprayed into the gas stream near the bottom of the vessel, and a second aqueous slurry is sprayed into the gas stream near the top of the vessel. 10. The method of claim 9, wherein each spray slurry is atomized into streams, yet each atomized slurry is collected separately.

14. The method of claim 13, wherein the water is sprayed into the gas stream over the second aqueous slurry spray in the vessel, and the spray water is collected with the second aqueous slurry.

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a first circulation system (coolant circulation system) for flue gas desulfurization that optimizes the use of make-up water while controlling slurry concentration for SO, cleaning efficiency and cooling. The second circulation system (absorbent circulation system) is a unique double circulation system,
This invention relates to a method of operating a gas flow cooler-absorber using a cleaning method.

The method of cleaning reboiler flue gases with a slurry containing alkaline solids such as limestone (CaCOJ) or calcined limestone products, lime and hydrated lime is well known for the removal of sulfur dioxide gas (SO2) from these combustion gases. It's a method.
However, standard cleaning methods require significant amounts of make-up water to operate, thereby increasing the water requirements of the overall system. Because water of adequate quality is often available in limited quantities in equipment, cleaning methods require the use of a minimum amount of high quality make-up or reuse water.
The sulfur dioxide scrubbing process requires make-up water to replace water lost primarily in two ways.

(1) water lost by evaporation due to cooling and temperature reduction of the flue gases passing through the washer; and (2) unreacted drug, calcium sulfite hydrate, and calcium sulfate hydrate discharged from the system. water that is lost with the discharge of solid waste consisting of a slurry of waste. Therefore, by reducing these water losses, the total replenishment water requirement to the system can be minimized. By controlling the circulating water from the dewatering system and selectively using high and low solids content slurry streams from the second circulation system (absorbent circulation system), we
It has been discovered that the first aqueous slurry (coolant slurry) concentration can be controlled and the requirement for new make-up water can be reduced.

In a dual circulation process, the main absorber system, including the scale-forming and corrosion-prone water droplet collector (Demister), is isolated from the evaporative cooler part of the process, and all circulating water is passed through the evaporative cooler circulation system. , but not to the circulatory system, which includes the water droplet collector and main absorber section. However, SO,
If the feed rate of the coolant circuit changes, the circulating water to the coolant circuit may be in excess or in deficit relative to the balance of evaporated matter in the coolant circuit. To compensate for either imbalance, a separator and flow control device is used between the two circuits to maintain a balanced flow rate of water into the coolant circuit while maintaining the absorbent circuit in proper operating balance. It is necessary to increase or decrease.
Generally, the composition of the slurry should be controlled so that the reaction product of calcium sulfite and calcium sulfate is greater than 3% in the coolant circulation system. Furthermore, for effective absorption of sulfur dioxide gas, the calcium base must be maintained above a minimum level. Typically the absorber is 6% to 1
It is operated at a solids content of 4%. The dual circulation process then makes the operation of the collector and main absorber part a completely open circulation system (0pen100p), so that contaminated circulating water is avoided and the use of additional collector wash water is avoided. Maximize.

Not using circulating water in these sections reduces shell formation, scale formation, and uncontrolled crystallization that would interfere with continuous operation of the SO2 removal system. This also reduces the use of expensive materials needed to prevent corrosion from dissolved chemicals such as chlorides. The use of circulating water from the dehydration system in the first circulation system, i.e. the coolant circulation system, reduces the operation of the entire system to a closed circulation system (ClOsedl).
OOp), so that all of the water used is used in the operation rather than being disposed of.

The present invention will be explained in further detail with reference to the drawings.

In FIG. 1 of the drawings, 10 generally indicates the system of the present invention, which system includes a multi-stage condenser-absorber column 12.
2 is shown in more detail in FIG. 2 and includes a cooler 14 and an absorber 16.

Arrows 18a, b, and c indicate cooler 1 from supply source 110, respectively.
4, the gas flow from the cooler 14 to the absorber 16 and the SO2 scrubbed flue gas from the absorber 16.

Other major components of this system include an absorbent tank 20;
It includes a coolant tank 22, a dehydration system 24, an absorbent separator 26, and pumps 28, 30 and 32, each of which has a pump designated 34a, b and c for pumps 32, 30 and 28, respectively. Has a sealed water inlet. The main liquid/slurry lines to the system are: line 36 from the absorbent tank 20 to the pump 28; line 38 comprising the first absorbent supply line from the pump 28 to the absorber 16; ; second absorbent supply pipe line 4 from absorbent tank 20 to pump 30;
0; second absorbent supply line 42 from pump 30 to absorber 16; line 44 consisting of a branch of line 42 from second absorbent supply line 42 to absorbent separator 26; from absorber 16; Pipe line 46 to absorbent tank 20: multi-stage cooler-absorber tower 1
Droplet collector wash water line 48 to 2; drug supply line 50 to absorbent tank 20; outlet line 52 from absorbent separator 26 to absorbent tank 20; outlet line from absorbent separator 26. Line 54: Line consisting of overflow line 56 of absorbent tank 20 to coolant tank 22; line 58 from coolant tank 22 to pump 32; coolant supply line from pump 32 to cooler 14. 60: A coolant return line 62 from the cooler 14 to the coolant tank 22; A line 64 consisting of a discharge pipe from the coolant tank 22 to the dehydration system 24 via the valve 10C; From the dehydration system 24 to the coolant tank 22 and a dehydration system discharge line 68 from the dehydration system 24 via valve 106''.

Referring now to FIG. 2, the multistage condenser-absorber tower 12 has a vertically extending shell 70 having a flue gas inlet 72 near its bottom and an SO2 scrubbed flue gas outlet 73 at its top.

Beneath the flue gas inlet 72 is a water sump 74, generally 7
A coolant tank is provided with a water sump agitation/agitation mechanism shown at 6. In FIG. 2, the cooler section is indicated generally at 14 and the absorber section is indicated generally at 16. The cooler section includes a number of headers 80 which connect to the line 60 from the pump 32, each header being provided with a number of spray outlet nozzles 82. In a preferred embodiment, cooler section 14 is tornado-shaped so that flue gases entering from inlet 72 flow tangentially upward.
The return line 62 shown in FIG. 1 is the gravity return of process fluid from the header 80 to the coolant tank 22. Between the cooler section 14 and the absorber section 16 there are typically 8
Gas/11quid pot separator (Gas/11quid) shown in 4.
b0w1separat0r). This separator 84
collects water from the droplet collector and slurry fluid from the absorber, with the collected fluid returning through line 46 from separator 84 to the absorbent tank. Above the bowl separator 84 are a number of headers, indicated at 86 and 86a, each of which has a first and a second absorbent feed line 38 and 42.
is connected to. Each of the headers 86 and 86a is provided with a number of spray-type outlet nozzles 88, and between the headers 86 and 86a is a conventional packed column apparatus.
ntiOnalpackedtOwerarrange
ment) 90.

A lower water droplet collector 92 and an upper water droplet collector 94 are arranged above the header 86a. Wash water for the lower droplet collector is supplied via a header 96 having a spray type outlet 98. The upper water droplet collector also has a spray type outlet 10.
A washing water means is provided including a header 100 with 2. Absorbent separator 26 and dehydration system 2 shown in FIG.
4 can take the form of a hydroclone, a concentrator, a centrifuge or a vacuum filter.

Again in the drawings of the invention, the dual circulation system includes the first circulation system (coolant circulation system) A, where almost all of the evaporative water loss occurs.
and a second circulation system (absorbent circulation system) B including water droplet collectors 92-94, in which case the gas first passes through the coolant circulation system and then the . The absorbent passes through the circulatory system.

The drug flow is in countercurrent to the gas flow and passes through the sorbent circulation system. Solids are removed from the system as follows; the solid reaction product between the calcium-based drug and the sulfur dioxide gas and a portion of the end-reacted drug are removed from the absorbent tank 20 of the absorbent ζ circulation system B. From there, through line 56, a rather constant concentration is supplied to the coolant circuit A together with some water.
The slurry also flows through line 44, absorbent separator 26 and line 54.
to the coolant circulation system A. The solids then circulate through coolant circuit A, where more reaction products are formed as the concentration of unreacted drug decreases. The solids are then discharged from the cooler to dewatering system 24 as final waste. Make-up water enters the absorbent circulation system by (1) water entering with the drug at 50; (2) a small amount of water for each slurry pump backing foot at 34c<5b; and (3) water droplets at 48. It enters as collector washing water.

Make-up water is also provided in the coolant circulation system: (1) a small amount of fresh make-up water at 34a and 34d for the slurry pump and agitator backings, respectively; (2) coolant make-up at 66 to replace most of the evaporative losses; water (circulated water); and (3) the absorbent circulation system at 56", which enters as 1 water that is agitated with the discharge solids. Process requirements for coolant make-up water are reflected in the sludge dewatering system
Optimum water utilization is achieved if the absorbent circulation system is filled with circulating water originating from the effluent.

If the produced circulating water exceeds the coolant make-up water requirement, the concentration of solids in the absorbent circulation system discharge slurry must be increased.

This is done by standard control in the absorbent separator 26. i.e. low-
10% to 50% while returning the solids stream to the absorbent tank 20.
A high solids stream having a solids content in the range of 50% flows through line 54 and mixes with the slurry flowing through line 56. The high solids content slurry is then discharged into the coolant circuit and the absorbent circuit is operated as an open system. Of course, if both circulatory systems are considered together, they constitute a closed circulatory system. These operating conditions, when the circulating water produced is less than the refrigerant make-up water requirement, include increasing the water content or reducing the low solids stream discharged from the separator 26 to the absorbent tank in line 5'. It is desirable to reduce the solids content in the absorber effluent by directing it to mix with the slurry.

At the same time, water may be added as droplet collector rinse water to the absorbent circulation system in proportion to the total fresh make-up water requirement.
As mentioned above, it is necessary to vary the amount of water discharged with the absorbent circuit discharge solids, ie, the discharge slurry concentration, without affecting the solids and drug balance of the absorbent circuit.

This is accomplished through the use of a solid-liquid separator 26 and commercially available control equipment. This equipment processes a portion of the absorbent circulation system slurry to produce two streams: a high solids stream and a low solids stream. Either or both of these streams are passed through one or more conduits 54 to a suitable amount of untreated absorbent circulation system slurry to create a stream 5' containing the desired concentration in the slurry entering the coolant tank 22. 56. This method allows a wide range of solids contents to be obtained from the absorber effluent. Since the operating conditions of the system, i.e. the charge factors and SO2 gas content, are constantly changing, the solids generation rate in the absorber circuit and the amount of water required to enter the cooler circuit are also changing.

Operating signals are used to adapt the absorber system to operational demands for water versus solids in the slurry. This signal changes the SO2 inflow to the absorber column, absorber slurry density, or other operation that changes the desired concentration of slurry effluent from the absorber circuit to the coolant tank with the varying SO2 flow to the absorber column. Related to the variables above. This signal is provided to a controller (not shown) to maintain the concentration of solids effluent to the cooler tank at a desired level.

[Brief explanation of the drawing]

FIG. 1 is a simplified diagram of the system of the present invention. FIG. 2 is a partially cut away schematic diagram of a multi-stage condenser-absorber column useful in implementing the system of the present invention. 12...Multi-stage cooler-absorber tower, 14...Cooler, 16...
...Absorber, 20...Absorbent tank, 22.
... Coolant tank, 24 ... Dehydration system, 2
6... Absorbent separator, 28, 30, 32... Pump, 50... Drug supply pipe to absorbent tank 20, 70... Outer wall, 72... ... Flue gas inlet, 80 ... Header, 84 ... Bowl separator, 86, 86a ... Header, 90 ...
... Packed tower device, 92,94 ... Water droplet collector, 96,100 ... Header.

Claims (1)

Claims: 1(a) cooling the gas stream in a first circulation system (coolant circulation system) with a first aqueous slurry containing an alkali; (b
) sending the effluent from the cooler to a coolant tank; (c) washing the gas stream to be cooled in a sulfur dioxide gas absorber with a second aqueous slurry containing an alkali, different from said first aqueous slurry; ( d) (1) separating the aqueous slurry discharged from the sulfur dioxide gas absorber into an overflow stream with a low solids content and an underflow stream with a high solids content in a liquid-solid separator; (2) high solids content of the second aqueous slurry; (3) continuously dewatering a portion of the aqueous slurry in the coolant tank; (4) disposing of solids from the dewatering process while returning the water to the coolant tank; 5) The overflow stream of low solids content stream is sent to the absorbent tank for reuse and water and alkali are added to it as required to remove the high solids content and low solids content from the recycled water and separator. 1. A method of operating a gas stream cooler-absorber consisting of two circulation systems for scrubbing sulfur dioxide gas from a gas stream, comprising the step of regulating the selective utilization of a volume stream. 2. A patent claim in which the gas stream to be washed passes through a water droplet collector, the water droplet collector is rinsed with water, and the washing water from the water droplet collector is added to the effluent from the absorber in the second circulation system. The method described in item 1. 3. The method according to claim 1, wherein the alkaline reagent is lime or limestone. 4. The method of claim 1, wherein the solids content of the aqueous slurry in the sulfur dioxide gas absorber is maintained at 6-14% solids content. 5. The high solids content stream from the separation step has a solids content in the range from 10 to 50%, and the low solids content stream has a solids content in the range from 3 to 10%. the method of. 6 The alkaline solid consists of CaCO_3 and is used in the above step [
d-(4)] in which the solids disposed of are primarily calcium sulfate. 7. The method of claim 1, wherein the low solids content stream from step [d] is primarily water and calcium carbonate. 8. The method of claim 5, wherein the high solids content understream is primarily water, calcium sulfite and calcium sulfate. 9(a) in a first circulation system (coolant circulation system), cooling the gas stream with a first aqueous slurry containing alkaline solids;
(b) in a second circulation system (absorbent circulation system) the gas stream to be cooled is washed with a second aqueous slurry containing alkaline solids separate from the first aqueous slurry; (c) an alkali in the second aqueous slurry; (d) maintaining the solids content at a level of 6-14% depending on the sulfur dioxide gas content in the gas stream by adding one or both of alkali solids and water; (d) alkali in the first aqueous slurry; The solids content is determined by the sulfur dioxide gas content in the gas stream.
% or more of sulfur dioxide gas from a gas stream comprising the step of retaining one or both of alkali solids and water from a second aqueous slurry portion having an alkali solids content higher or lower than said level. A method of operating a gas flow cooler-absorber comprising two circulation systems according to claim 1 for cleaning. 10 The alkaline solids consist of CaCO_3, and a concentrated slurry of fresh water and alkaline solids is introduced into the second aqueous slurry, and the circulating slurry avoids the formation of dissolved calcium sulfate compounds in the second aqueous slurry and substantially maintains the open second slurry. 10. The method of claim 9, wherein the second aqueous slurry is removed and introduced into the first aqueous slurry to form a two-circulation system. 11 The slurry is mixed from the second aqueous slurry to the first aqueous slurry to partially replace the slurry lost in the cooling process.
Claim 1: Continuously supplied to the aqueous slurry
The method described in item 0. 12. The method of claim 11, wherein the first aqueous slurry and the second aqueous slurry are circulated in separate cooling and cleaning circuits. 13 The cleaning of the gas stream is carried out in a closed vessel where the gas enters at the bottom and exits at the top, a first aqueous slurry is sprayed into the gas stream near the bottom of the vessel and a second aqueous slurry is sprayed into the gas stream near the top of the vessel. 10. The method of claim 9, wherein each spray slurry is atomized into streams, yet each atomized slurry is collected separately. 14. The method of claim 13, wherein water is sprayed into the gas stream over the second aqueous slurry spray in the vessel, and the spray water is collected with the second aqueous slurry.